1. Field of the Invention
This invention relates to a radiation image read-out apparatus provided with a film digitizer for photoelectrically reading out a radiation image, which has been recorded on a sheet of silver halide film, and thereby generating an image signal representing the radiation image.
2. Description of the Prior Art
Techniques for reading out a recorded image in order to obtain an image signal, carrying out appropriate image processing on the image signal, and then reproducing a visible image by use of the processed image signal have heretofore been known in various fields.
For example, as disclosed in Japanese Patent Publication No. 61(1986)-5193, a sheet of X-ray film having a small gamma value chosen according to the type of image processing to be carried out is used together with an intensifying screen, and an X-ray image is recorded on the X-ray film. The X-ray film, on which the X-ray image has been recorded, is subjected to a developing process. The X-ray image is then read out from the X-ray film and converted into an electric signal (image signal). The image signal is processed and then used for reproducing the X-ray image as a visible image on a copy photograph or the like. In this manner, a visible image having good image quality with high contrast, high sharpness, high graininess, or the like, can be reproduced. The device for detecting the image signal from the film is usually referred to as a film digitizer (FD).
When certain kinds of phosphors are exposed to radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the amount of energy stored thereon during its exposure to the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318, 4,387,428, and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to radiation which has passed through an object, such as the human body. A radiation image of the object is thereby stored on the stimulable phosphor sheet. The stimulable phosphor sheet is then scanned with stimulating rays, such as a laser beam, which cause it to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal. The image signal is then used during the reproduction of the radiation image of the object as a visible image on a recording material such as photographic film, on a display device such as a cathode ray tube (CRT) display device, or the like. Such radiation image recording and reproducing systems are usually referred to as computed radiography (CR).
CR systems which use stimulable phosphor sheets are advantageous over conventional radiography using silver halide photographic materials, in that images can be recorded even when the energy intensity of the radiation to which the stimulable phosphor sheet is exposed varies over a wide range. More specifically, since the amount of light which the stimulable phosphor sheet emits when being stimulated varies over a wide range and is proportional to the amount of energy stored thereon during its exposure to the radiation, it is possible to obtain an image having a desirable density regardless of the energy intensity of the radiation to which the stimulable phosphor sheet was exposed. In order to obtain the desired image density, an appropriate read-out gain is set when the emitted light is being detected and converted into an electric signal to be used in the reproduction of a visible image on a recording material, such as photographic film, or on a display device, such as a CRT display device.
The film digitizer systems (FD systems), which use X-ray film, and the computed radiography systems (CR systems), which use stimulable phosphor sheets, have been developed independently of each other. Therefore, in the past, no problem occurred from incompatibility between the FD systems and the CR systems.
However, recently, in a single large hospital, it often occurs that an FD system, which uses X-ray film, is introduced into a certain medical office, and a CR system, which uses stimulable phosphor sheets, is introduced into a different medical office. Also, it often occurs that an FD system, which uses X-ray film, is introduced into a certain hospital, and a CR system, which uses stimulable phosphor sheets, is introduced into a different hospital. In such cases, problems occur in that information interchange cannot be carried out smoothly between the medical office, into which the FD system has been introduced, and the medical office, into which the CR system has been introduced. Such problems also occur between the hospital, into which the FD system has been introduced and the hospital, into which the CR system has been introduced.